全文获取类型
收费全文 | 1966篇 |
免费 | 40篇 |
国内免费 | 6篇 |
专业分类
化学 | 1371篇 |
晶体学 | 30篇 |
力学 | 43篇 |
数学 | 335篇 |
物理学 | 233篇 |
出版年
2022年 | 18篇 |
2021年 | 15篇 |
2020年 | 26篇 |
2019年 | 21篇 |
2016年 | 23篇 |
2015年 | 27篇 |
2014年 | 35篇 |
2013年 | 70篇 |
2012年 | 62篇 |
2011年 | 95篇 |
2010年 | 40篇 |
2009年 | 42篇 |
2008年 | 84篇 |
2007年 | 95篇 |
2006年 | 82篇 |
2005年 | 68篇 |
2004年 | 69篇 |
2003年 | 73篇 |
2002年 | 63篇 |
2001年 | 26篇 |
2000年 | 18篇 |
1999年 | 16篇 |
1998年 | 22篇 |
1997年 | 26篇 |
1996年 | 42篇 |
1995年 | 30篇 |
1994年 | 24篇 |
1993年 | 25篇 |
1992年 | 25篇 |
1991年 | 18篇 |
1990年 | 20篇 |
1989年 | 25篇 |
1988年 | 19篇 |
1987年 | 28篇 |
1986年 | 21篇 |
1985年 | 42篇 |
1984年 | 38篇 |
1983年 | 36篇 |
1982年 | 37篇 |
1981年 | 31篇 |
1980年 | 13篇 |
1979年 | 27篇 |
1978年 | 38篇 |
1977年 | 32篇 |
1976年 | 33篇 |
1975年 | 35篇 |
1974年 | 23篇 |
1973年 | 20篇 |
1972年 | 13篇 |
1966年 | 16篇 |
排序方式: 共有2012条查询结果,搜索用时 359 毫秒
161.
We study analytically the approach to equilibrium in a simple zero-temperature model for phase separation in a binary alloy, in which nearest neighbor interchange can occur only if the portion of AB bonds is thereby decreased. The approach to equilibrium is found analytically. Because of the existence of infinitely many possible stationary states, the asymptotic distribution of AB pairs depends on the details of the initial state and must be obtained by a recursion method.Chargé de recherches FNRS. 相似文献
162.
163.
164.
Dr. Sara Sabater Dr. David Schmidt Dr. Heidi Schmidt Dr. Maximilian W. Kuntze-Fechner Dr. Thomas Zell Connie J. Isaac Dr. Nasir A. Rajabi Harry Grieve Dr. William J. M. Blackaby Dr. John P. Lowe Prof. Stuart A. Macgregor Dr. Mary F. Mahon Prof. Dr. Udo Radius Prof. Michael K. Whittlesey 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(52):13221-13234
The addition of PPh2H, PPhMeH, PPhH2, P(para-Tol)H2, PMesH2 and PH3 to the two-coordinate Ni0 N-heterocyclic carbene species [Ni(NHC)2] (NHC=IiPr2, IMe4, IEt2Me2) affords a series of mononuclear, terminal phosphido nickel complexes. Structural characterisation of nine of these compounds shows that they have unusual trans [H−Ni−PR2] or novel trans [R2P−Ni−PR2] geometries. The bis-phosphido complexes are more accessible when smaller NHCs (IMe4>IEt2Me2>IiPr2) and phosphines are employed. P−P activation of the diphosphines R2P−PR2 (R2=Ph2, PhMe) provides an alternative route to some of the [Ni(NHC)2(PR2)2] complexes. DFT calculations capture these trends with P−H bond activation proceeding from unconventional phosphine adducts in which the H substituent bridges the Ni−P bond. P−P bond activation from [Ni(NHC)2(Ph2P−PPh2)] adducts proceeds with computed barriers below 10 kcal mol−1. The ability of the [Ni(NHC)2] moiety to afford isolable terminal phosphido products reflects the stability of the Ni−NHC bond that prevents ligand dissociation and onward reaction. 相似文献
165.
Heavy tailed durations of regional rainfall 总被引:1,自引:0,他引:1
Durations of rain events and drought events over a given region provide important information about the water resources of
the region. Of particular interest is the shape of upper tails of the probability distributions of such durations. Recent
research suggests that the underlying probability distributions of such durations have heavy tails of hyperbolic type, across
a wide range of spatial scales from 2 km to 120 km. These findings are based on radar measurements of spatially averaged rain
rate (SARR) over a tropical oceanic region. The present work performs a nonparametric inference on the Pareto tail-index of
wet and dry durations at each of those spatial scales, based on the same data, and compares it with conclusions based on the
classical Hill estimator. The results are compared and discussed.
The authors express sincere thanks to the Mathematisches Forschungsinstitut Oberwolfach (MFO) for facilitating their collaboration
under a “Research in Pairs” project hosted at MFO during March 5–25, 2006. The research of the second and third authors was supported by the project
LC06024. 相似文献
166.
The influence of nucleus density on optical properties in nucleated isotactic polypropylene 总被引:1,自引:0,他引:1
Alfrd Menyhrd Markus Gahleitner Jzsef Varga Klaus Bernreitner Pirjo Jskelinen Harry
ysd Bla Puknszky 《European Polymer Journal》2009,45(11):3138-3148
The effect and efficiency of three nucleating agents, a sorbitol based clarifier, a traditional heterogeneous nucleating agent and poly(vinylcyclohexane) (PVCH) was studied in polypropylene (iPP) homopolymer. The nucleating agents were added to iPP in different amounts; PVCH in 0–200 ppm, while the other two in 0–2000 ppm. Optical and mechanical properties were determined on injection molded plates or bars, respectively. Nucleation efficiency was studied by thermal analysis, while structure was characterized by polarized light (PLM), scanning electron (SEM) and atomic force microscopy (AFM). Nucleus density was calculated using the method of Lamberti, which is based on the kinetic theory of the crystallization developed by Lauritzen and Hoffmann. The results proved that the nucleating agents modify properties in different ways and extent. PVCH is very efficient already at small concentrations and increases the stiffness of iPP considerably more than the other two compounds. On the other hand, the clarifier and the traditional nucleating agent induce better optical properties even at smaller efficiency. The structure developing in the presence of the three nucleating agents is also different. The clarifier forms a network in iPP and induces the formation of a microcrystalline structure according to the former literature data. Microspherulitic structure develops in the presence of the heterogeneous nucleating agent studied, while relatively large supermolecular units form in iPP nucleated by PVCH even under the conditions of injection molding. The calculation of nucleus density by existing models and the comparison of the results to optical properties proved that haze is determined by the size of the supermolecular units of the polymer and this latter depends on nucleus density. 相似文献
167.
Harry C. Jones 《Fresenius' Journal of Analytical Chemistry》1896,35(1):90-91
Ohne Zusammenfassung 相似文献
168.
169.
170.
Xiangrong Xu Lee Koetzner Jamie Boulet Harry Maselli Jessica Beyenhof Gary Grover 《Biomedical chromatography : BMC》2009,23(9):973-979
A simple and sensitive analytical method using liquid chromatography–tandem mass spectrometry (LC/MS/MS) for determination of acetylsalicylic acid (aspirin, ASA) and its major metabolite, salicylic acid (SA), in animal plasma has been developed and validated. Both ASA and SA in plasma samples containing potassium fluoride were extracted using acetonitrile (protein precipitation) with 0.1% formic acid in it. 6‐Methoxysalicylic acid was used as the internal standard (IS). The compounds were separated on a reversed‐phase column. The multiple reaction monitoring mode was used with ion transitions of m/z 178.9 → 136.8, 137.0 → 93.0 and 167.0 → 123.0 for ASA, SA and IS, respectively. The lower limits of quantification for ASA and SA were 3 and 30 ng/mL, respectively. The developed method was successfully applied for the evaluation of pharmacokinetics of ASA and SA after p.o. and i.v. administration of 1 mg/kg to rats. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献